Adjustable resistors and method of making the same



Jan. 1, 1963 J. E. STARR ADJUSTABLE RESISTORS AND METHOD OF MAKING THESAME Filed May 1'7, 1960 HIIIIIIHIH IIIHIIIIH 1. INVENToR. James E.Siarr WIR A TTORNE Y United States Patent Chlice 3,017 1,749 Patented .lan. 1, 1963 3,tl71,749 ADJUSTABLE RESISTORS AND METHGD F MAKING THE SAMEJames E. Starr, Norristown, Pa., assigner to The Budd Company,Philadelphia, Pa., a corporation of Penn- Sylvania Filed May 17, 1960,Ser. No. 29,711 13 Claims. ((l. 338-314) This invention relates toadjustable resistors and method of making the same and has for an objectthe provision of improvements in this art.

One of the specific objects of the invention is to provide an adjustableresistor which can readily have yits resistance decreased as well asincreased.

Another object is to provide a resistor which has a good heat sink tomaintain a uniform temperature and resistance in use.

Another object is to provide ak metal backing plate with a solderconnection to a superposed insulated resistor to hold the resistor fastat the point of connection.

Another object is to provide a construction which is subject to quickand easy resistance selection.

' Another object is to provide a simple and convenient method ofadjusting the resistance of a resistor.

Another object is to provide a resistor which can have its resistancechanged without affecting its external connections or the leadstherefor.

The above and other objects and advantages of the invention and variousfeatures of novelty will be apparent from the accompanying descriptionof an exemplary erna, bodiment, reference being made to the accompanyingdrawings wherein:

FIG. l is a plan view of one form of resistor unit ernbodying theinvention;

FG. 2 isa cross-section of the resistor unit, the section being taken onthe line 2-2 of FIG. l; and

FIG. 3 is a plan view of another embodiment.

Resistors formed ot metal foils`orkilms have many advantages over wireor other types. Among these advantages is an extensive surface forbonding to a supporting body and for transferring heat to air or to anadjacent heat sink such as a supporting plate or body. Heat dissipationis improved by having a thin insulating layer support for the resistor;and a foily or ilm permits an insulating layer of minimum thickness tobe used with the least danger of rupture and short-circuiting.

Another advantage of the foil type resistor is the 'ease in which theresistance value can be varied by thinning or narrowing the elements ofthe pattern. Either chemical etching or mechanical reduction of thewidth orV thickness to increase the resistance are easily accomplished.The reduction in thickness which may be practically attained with a foilresistor without impairing the performance ofthe resistor is about 30%Heretofore after a foil resistor was made, as by the photographicpattern printing and etching process, it could only have its initial`resistance increased; it was impossible to decrease its resistance. Thepresent invention makes it possible to decrease the resistance to anydesired extent and then, if desired, to increase the selected resistanceto attain a tinal resistance valve of high accuracy.

With the herein described resistance unit and method it is possible toachieve great economy and convenience by makingresistor units of certainranges and readily bringing them to specific precision resistance valuesfor use `or sale. Thereby with a very small stock range it is possibleto supply an unlimited range of unit resistance values.

As shown in the drawings, a resistor foil atterri or grid 1l) is formed,as by a photographic printing and such as 18, directly to the surface ofthe resistor.

chemical etching process, and adhesively bonded to a thin insulatinglayer 11, as of suitable plastic. The plastic layer may follow the foilfrom its solid free sheet shape through its forming processes or mayhave the formed foil pattern transferred to it after formation or atsome time during its for-mation. An insulating layer of good dielectricproperties and shape stability throughout its range of use is verydesirable and epoxy or glass fabric have been found suitable. Theinsulation is one which can be scraped off locally or punched througheasily for making a solder connection as will be described hereinafter.

The insulating layer 11 is secured, as by adhesive bonding, to a metalsheet 12 of good electrical and heat conductivity, such as copper,aluminum or the like. For some uses, as where the metal sheet is thickenough to be an adequate heat sink for the heat created in the use ofthe resistor unit, the one metal sheet may be sufficient; but herein itis shown `to be relatively thin and to be secured, with an interveninginsulating layer 13, to a heavier metal sheet or plate 14 which providesa heat sink of much greater capacity. If the resistor unit is in servicemounted on a metal base then this base will form the heat sink. Y

When desirable, the unit may be mounted and secured, as by adhesive, onkan insulating carrier sheet, plate or substrate 15.

The resistor grid 1d, at one end is provided with a lead tab 16 and inservice a lead 17 is connected, as by soldering, to this tab. This leadmay bevconnected in the field; or, since the connection requires adelicate operation, a short lead of material heavier than the foil maybe connected at the ltime of manufacture.

To the meta-l sheet 12 there is secured, as by solder, a lead 18. Thisconnection is less delicate than the other but, if desired, may be madeat the time of manufacture and covered by insulation except at aprotruding end.

To make a resistor unit of any selected Vresistance possible with `theinitial grid or patterna spot is selected for a predetermined resistanceValue l.along the elements ot the grid and the underlying insulationscraped away and a solder connection 2t) made between the grid elementand the metal sheet 12. Scale markers 21 may be formed from the originalfoil sheet along with the grid to indicate values along the pattern. l

The sheet 12 is relatively so thick and so highly conductive that it, ineffect, forms a direct electrical connection from its lead 18 to anypoint over its area at which the connection 20 is made.

If a pointed soldering tool is used it may serve both to rupturethefinsulation and to make the solder connection instead of having toscrape away the insulation as a separate operation. A pointed solderingtool 22 is indicated in broken lines in FIG. 2.

In some cases it may be desirable to connect a lead, If so, it Vis stilldesirable to make the solder joint through the insulation from theresistor to the metalplate. This provides a firm anchorage at thispoint. Alternatively a connection maybe made to the metal plate by moredirect means such as mounting the plate on a conductor or mounting aconductor on the plate.

IA great variety of resistor units may be made by the present invention.One other example is shown in FIG. 3 where leads 17 and 1S lare providedas before but wherey the grid has a lead tab 16a and a lead 17a at itsother end and the connection 20 divides the total resistance of the gridinto selected relative Vvalues as before, the solder joint 2d is usefulas an anchorage for the foil to a substantial body even if the lead 18'is connected directly to the foil instead of to the Imetal plate. Afterthe solder connection 2t) or 20 has been made to establish the minimumresistance, selected to be slightly lower than the desired finalresistance value, the resistance is increased up to the exact desiredvalue by decreasing the cross section of the active portion of thepattern, carefully measuring the resistance by instruments as theadjustment proceeds. As stated above, the cross section can be reducedin various ways. One simple way is to rub the top surface evenly with alight abrasive like pumice or rouge with the finger tip or a smallrubbing tool. Skilled workers become very adept at this operation evenwith resistors of very small size.

It is thus seen that the invention provides an improved adjustablehigh-precision resistor and an improved method of forming it. p

While one embodiment of the invention has been described for purposes ofillustration it is to be understood that there may be variousembodiments and modifications within the scope of the invention.

What is claimed is:

l. A printed circuit resistor unit comprising in combination, a foilresistor pattern, a thin plastic insulating layer supporting and bondedto one side of said resistor pattern, a continuous metal sheet bonded tothe other side of said insulating layer, said metal sheet being of amaterial of good electrical and heat conductive material to constitute acommon potential area and heat sink, an electrical conductor leadconnected to said resistor pattern, and a solder connection between saidresistor pattern and said metal sheet through said thin plasticinsulating layer at a calibrated point spaced from the lead connected onthe pattern electrically connecting said metal sheet to said electricalconductor lead with a prtion of said resistor pattern in seriestherebetween. v

2. A printed circuit resistor unit as set forth in claim 1, whichfurther includes a heavier metal body bonded to and insulated from saidmetal sheet to act as a heat sink of greater capacity.

3. A resistor unit comprising in combination, a Vmetal sheet ofnegligible resistance, of good heat conductivity and of sufficientthickness to constitute a good heat sink, an insulation layer bonded tosaid metal sheet, a resistor pattern bonded to the other side of saidlayer of insulating material, said layer being very thin and easilypierced, a solder connection between the pattern and sheet, a conductorlead connected to said metal sheet, and at least one conductor leadconnected to one end of said pattern, the unit being adapted to havesaid solder connection made between said pattern and said metal sheetthrough said insulating layer at a selected point along the patternelectrically connecting said metal sheet and an electrical conductorlead on said pattern with a portion of said resistor pattern in seriestherebetween.

4. A resistor unit comprising in combination, a metal sheet, aninsulation layer bonded to said metal sheet, a resistor pattern bondedto the other side of said insulating layer, said pattern being freelyaccessible on one side, spaced leads connected to said pattern, and asolder connection between said sheet and pattern through said insulatinglayer at a point between the leads connected to said pattern, whereby aconnection to said sheet and one of said leads defines a precisionresistance path.

5. The method of making a resistor unit which cornprises, bonding a fiatfoil resistor pattern having at least one lead connection alixed theretoto one side of a metal heat sink sheet with a thin sheet of insulationtherebetween, connecting a lead to said metal sheet, and making anelectrical solder connection between said resistor pattern and saidmetal sheet through said insulation at a measured point spaced from thepattern lead to connect a portion of said resistor pattern between saidpattern lead and said lead on said metal sheet.

6. The method as set forth in claim 5, which further includes the stepof'reducing aportion of the cross section of the pattern between thepattern lead and electrical connection to make a line adjustment in therei sistance value by increasing it after the lead and electricalconnections have been made to establish an initial minimum resistance insaid pattern.

7. The method as set forth in claim 5, which further includes the stepof connecting two spaced leads to said pattern before the electricalconnection is made and making the electrical connection at a selectedpoint between said leads.

8. The method as set forth in claim 6, which further includes the stepof reducing the cross section of the pattern between one of said leadsand said electrical connection after the electrical connection has beenmade.

9. The method of making a resistor unit which comprises, forming on aninsulating sheet a resistor pattern from a foil sheet by thephotographic printing and chemical etching or milling process, bondingthe foil pattern and insulation to a metal conducting and heat sinksheet, making lead connections to said metal sheet and pattern, andmaking an electrical solder connection from said pattern to said metalsheet through said insulation at a point spaced from a lead connected tothe pattern.

10. The method as set forth in claim 9 which further includes the stepof reducing a portion of the cross section and increasing the resistanceof the useful length of the foil pattern by thinning it by abrasion onthe top surface.

11. The method of making precision printed `circuit resistors whichcomprises the steps of: making a printed circuit type grid pattern on athin calibrated insulation layer mounted on an electrically conductivesheet, said pattern having a resistance value greater than the desiredprecision value, connecting a lead to said pattern, connecting anotherlead to said sheet, making a solder connection through said thininsulation to electrically connect a point on said pattern with saidsheet to define a predetermined calibrated length of said grid patternbetween said leads,.and reducing a portion of said calibrated length byabrasive action while carefully measuring the resistance until apredetermined precision value is reached.

l2. The method of making a precision temperature compensating printedcircuit resistor which comprises: :forming a bonded laminate of a heatsink metal sheet, a thin insulation layer, and a flat foil patternresistance grid; making at least two lead connections to said patternspaced apart to define a predetermined portion of said patternresistance grid; removing a portion of said resistance whilesimultaneously measuring the resistance value until a desired precisionval-ue is obtained; and making solder connections from said patternresistance grid through said insulation layer to said metal sheet atpoints along said grid outside said predetermined portion of saidpattren resistance grid. Y

13. The method of making precision printed circuit resistors comprisingthe steps of making a flat thin printed circuit metal grid resistor onone side of an insulating sheet, said insulation sheet having a metallicconductive sheet bonded to the other side of said insulating sheet,connecting leads to said conductive sheet and said printed circuit,making a Solder connection between a point on said resistor and saidinsulating sheet by piercing the insulation, measuring the resistance ofthe path between any pair of said leads, and increasing said measuredre-v sistance by abrasive action removal of a portion of said gridresistor.

References Cited in the file of this patent UNITED STATES PATENTS1,930,932 Freyman Oct. 17, 1933 1,962,438 Flanzer et al. .lune 12, 19341,970,051 McWeeny Aug. 14, 1934 2,474,988 Sargrove July 5, 19492,482,316 Bocking Sept. 20, 1949 2,518,941 Satchwell et al. Aug. 15,1950 2,939,807 Needham June 7, 1960

1. A PRINTED CIRCUIT RESISTOR UNIT COMPRISING IN COMBINATION, A FOILRESISTOR PATTERN, A THIN PLASTIC INSULATING LAYER SUPPORTING AND BONDEDTO ONE SIDE OF SAID RESISTOR PATTERN, A CONTINUOUS METAL SHEET BONDED TOTHE OTHER SIDE OF SAID INSULATING LAYER, SAID METAL SHEET BEING OF AMATERIAL OF GOOD ELECTRICAL AND HEAT CONDUCTIVE MATERIAL TO CONSTITUTE ACOMMON POTENTIAL AREA AND HEAT SINK, AN ELECTRICAL CONDUCTOR LEADCONNECTED TO SAID RESISTOR PATTERN, AND A SOLDER CONNECTION BETWEEN SAIDRESISTOR PATTERN AND SAID METAL SHEET THROUGH SAID THIN PLASTICINSULATING LAYER AT A CALIBRATED POINT SPACED FROM THE LEAD CONNECTED ONTHE PATTERN ELECTRICALLY CONNECTING SAID METAL SHEET TO SAID ELECTRICALCONDUCTOR LEAD WITH A PORTION OF SAID RESISTOR PATTERN IN SERIESTHEREBETWEEN.